linux-kernel - Re: [PATCH] nvme: utilize two queue maps, one for reads and one for writes

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Date:   Tue, 13 Nov 2018 17:51:08 -0700
From:   Jens Axboe <axboe@...nel.dk>
To:     Guenter Roeck <linux@...ck-us.net>
Cc:     Keith Busch <keith.busch@...el.com>,
        Sagi Grimberg <sagi@...mberg.me>,
        linux-nvme@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] nvme: utilize two queue maps, one for reads and one for
 writes

On 11/13/18 5:41 PM, Guenter Roeck wrote:
> Hi,
> 
> On Wed, Oct 31, 2018 at 08:36:31AM -0600, Jens Axboe wrote:
>> NVMe does round-robin between queues by default, which means that
>> sharing a queue map for both reads and writes can be problematic
>> in terms of read servicing. It's much easier to flood the queue
>> with writes and reduce the read servicing.
>>
>> Implement two queue maps, one for reads and one for writes. The
>> write queue count is configurable through the 'write_queues'
>> parameter.
>>
>> By default, we retain the previous behavior of having a single
>> queue set, shared between reads and writes. Setting 'write_queues'
>> to a non-zero value will create two queue sets, one for reads and
>> one for writes, the latter using the configurable number of
>> queues (hardware queue counts permitting).
>>
>> Reviewed-by: Hannes Reinecke <hare@...e.com>
>> Reviewed-by: Keith Busch <keith.busch@...el.com>
>> Signed-off-by: Jens Axboe <axboe@...nel.dk>
> 
> This patch causes hangs when running recent versions of
> -next with several architectures; see the -next column at
> kerneltests.org/builders for details.  Bisect log below; this
> was run with qemu on alpha. Reverting this patch as well as
> "nvme: add separate poll queue map" fixes the problem.

I don't see anything related to what hung, the trace, and so on.
Can you clue me in? Where are the test results with dmesg?

How to reproduce?

-- 
Jens Axboe